This invention relates to a phenolic resin composition useful for preparing fiberglass insulation. The present invention particularly relates to phenolic resins having formaldehyde to phenol molar ratios of greater than 3.75:1. These resins are used to fabricate formaldehyde/phenol urea extended binders that have high urea extension levels.
Polymeric fiberglass binders have a variety of uses ranging from stiffening applications where the binder is applied to woven or non-woven fiberglass sheet goods and cured producing a stiffer product; thermoforming applications wherein the binder resin is applied to sheet or lofty fibrous product following which it is dried and optionally B-staged to form an intermediate by yet curable product; and to fully cured systems such as building insulation, wherein the binder is fully cured to its thermoset state while the fiberglass is in the fully expanded condition, following which the rolls or batts are compressed for storage and shipment.
Fiberglass comes in many shapes and sizes and can be used for a variety of applications. A general discussion of fiberglass manufacturing and technology is contained in Fiberglass by J. Gilbert Mohr and William P. Rowe (Van Nostrand Reinhold Company, New York 1978), which is herein incorporated by reference. Fiberglass which is destined for use as insulation, e.g., building, mechanical or the like for thermal or sound attenuation, is often shipped in a compressed form to lower shipping costs. When the compressed bundles of fiberglass are utilized at the job site, it is imperative that the fiberglass product recover a substantial amount of its precompressed thickness. Otherwise, loss of thermal insulation and sound attenuation properties may result.
Traditionally, fiberglass has been treated with phenol/formaldehyde resole binders to achieve the previously discussed recovery from compression. Typically, the binders are applied to the fiberglass from aqueous solution shortly after the fibers have been produced, and cured at elevated temperature in a curing oven. Under the curing conditions, any remaining aqueous solvent is evaporated, and the phenol/formaldehyde resole cures to a thermoset state. The fibers in the resulting fiberglass product are thus partially coated with a thin layer of thermoset resin, which tends to accumulate at the junctions where fibers cross each other. The resulting product therefore not only exhibits higher recovery than a fiberglass product not incorporating a binder, but also suffers from less self-abrasion.
Resins for the fiberglass industry are water soluble; this requirement necessitates high starting formaldehyde to phenol ratios in the resin manufacturing process. Typical formaldehyde to phenol ratios are in the range of 2.5:1 to 3.5:1. The finished phenolic resins used by the fiberglass industry have between approximately 3 and 13 wt % free formaldehyde remaining. This excess of formaldehyde has been taken advantage of by adding urea to the phenol/formaldehyde resole, resulting in a urea-extended resole. The addition of urea to the resins typically occurs 6 to 18 hours before use to form urea/formaldehyde resin in situ in a process known as pre-reaction. This technique reduces the formaldehyde content and significantly lowers the cost of the finished binder. The exact excess of formaldehyde in the phenol/formaldehyde resins that are purchased is dictated by the cost reduction required versus the degradation in binder performance as the urea/formaldehyde content is increased. The latter is based on greater ammonia and particulate emissions as the urea content is increased. Generally, a resin designed to have enough xe2x80x9cfreexe2x80x9d formaldehyde to react with 30 parts by weight of urea per 70 parts of resin solids is seen as being a good compromise for a building insulation product. The binder resulting from this pre-reaction is known as a 70/30 extended binder. For other types of product, such as fiberglass air filter media, much less urea can be tolerated and so resins with formaldehyde contents as low as 3.5 wt % may be used. In the latter cases the extended binders may use resin solids to urea ratios as low as 95/5. Urea pre-reaction consumes much of the formaldehyde but it is thought that an equilibrium amount of between 0.5 and 1 wt % always remains.
Currently, typical fiberglass building insulation processes use resins requiring 30-40 wt % urea extension levels. These levels are established by calculating the formaldehyde to urea molar ratio, which is about 1:1. The molar ratio of free formaldehyde in the resin to urea must be carefully controlled in order to minimize both ammonia and formaldehyde emissions. In many building insulation binders this molar ratio is kept between 0.8 and 1.0. If the ratio drops below 0.8, ammonia emissions increase significantly, likewise if the ratio rises above 1.0, formaldehyde emissions increase significantly. As a result, building insulation resins generally contain between 10 and 12 wt % free formaldehyde. This allows these resins to be reacted with between 30 and 40 wt % urea on a solid weight percent basis. This range of urea extension has been demonstrated to give good performance in terms of the binder resistance to hydrolysis under conditions of high heat and humidity, thereby maintaining product performance in terms of rigidity and recovered thickness. The cost of the phenolic resin in the pre-mix is approximately three times that of the urea. Therefore, using higher extension binders will lower cost. However, it is commonly believed that too much urea results in degradation of product quality. Common commercial phenol/ formaldehyde binders are not available with greater than about 12.5 wt % free formaldehyde which limits the urea extension to a maximum of 40 wt % while maintaining the desired formaldehyde to urea molar ratio of from 0.8 to 1.0. Since pre-reaction decreases the cost of the finished binder, it would be beneficial to develop phenolic resins having higher free formaldehyde levels that can be employed to form higher urea extension binders.
The present invention relates to binders of phenol/formaldehyde resin and urea wherein the resin to urea solids ratio is below 60/40. Employing the inventive binders in the production of fiberglass products reduces manufacturing costs without adversely affecting product performance or increasing formaldehyde or ammonia emissions. Specifically, the invention relates to the use of urea extended phenolic binders with a resin to urea solids ratio below 60/40. The phenolic resins are prepared in a reaction in which the formaldehyde and phenol are initially present in mole ratios of greater than 3.75:1. The use of a high formaldehyde to phenol ratio reduces the cost of the phenol resin and ultimately the extended phenolic binder because formaldehyde is much less expensive than phenol. The high extension level binders are particularly suited for making fiberglass building insulation.
In one aspect, the invention is directed to a method of preparing a binder suitable for treating fiberglass that includes the steps of:
(a) selecting an aqueous resin prepared by reacting phenol with formaldehyde wherein the mole ratio of formaldehyde to phenol is greater than 3.75:1 under alkaline conditions; and
(b) adding urea to the aqueous resin in an amount greater than 40 parts per 60 parts of resin solids and reacting to form a urea-extended binder, wherein free phenol present in the urea-extended binder is less than about 1% by weight of urea-extended binder and wherein essentially no ammonia is employed in either step (a) or (b).
In another aspect, the invention is directed to an aqueous phenol/formaldehyde-based binder suitable for applying to fiberglass wherein the binder is prepared by a process that includes the steps of:
(a) selecting an aqueous resin prepared by reacting phenol with formaldehyde wherein the mole ratio of formaldehyde to phenol is greater than 3.75:1 under alkaline conditions; and
(b) adding urea to the aqueous resin in an amount greater than 40 parts per 60 parts of resin solids and reacting to form a urea-extended binder, wherein free phenol present in the urea-extended binder is less than about 1% by weight of urea-extended pre-react and wherein essentially no ammonia is employed in either step (a) or (b).
In preparing the phenol/formaldehyde based binder, the molar ratio of free formaldehyde to urea is preferably controlled in order to minimize emissions of ammonia and formaldehyde. Typically this molar ratio is kept between 0.8 and 1.0, therefore, higher free formaldehyde resins may be reacted with a higher percentage of urea to maintain the target formaldehyde to urea molar ratio.